Method of treating wells



retested dul as,

attests estates nurses or rename warns Allen is. Garrison, Houston, Tex,assiguor, by mesne assignments, to The Texas Company, New Yorls. N. Y.,a corporation or Delaware No Drawing. Application January 30, 1941,

Serial No. 376,652

14 Claims.

increase the ratio of oil relative to water pro-' duced from the well.

It is commonly recognized that oil producing sands are invariablywater-wet and that the adsorbed water films on the sand grainsfacilitate the flow of water and resist the flow of oil through theformation. This resistance to the oil flow limits the passage of the oilto the pore spaces of the larger interstices and even these pore spacesare reduced in volume by the water films on the adjoining sand grains,Where this condition is prevalent, the well produces both water and oil,and after some time the formation water advances toward the well boreand so completely blocks the interstices and capillary openings that itbecomes economically impos sible to produce oil from the well.

Heretofore it' has been found possible to re move the water film fromthe water-wet sand by depositing a preferential wetting agent in theform of a precipitate on the sand grains which renders themoil-wettable. In this manner the flow of water into the well is resistedby the same force which resists the flow of oil through the water-wetoil producing sand. This procedure is illustrated in Patent No.2,02,l19, issued to William V. Vietti and Allen D. Garrison, whichdiscloses and claims a method of treating a water-wet oil producing sendby depositing a water and oil insoluble precipitate on the sand grains,which precipitate is preferentially wettable by oil. In accordance withthe method of the patent an aqueous solution of an alkali metal salt ofa sulfonated oil, fat or fatty .acid is introduced into the well andinto the producing sand, and is either reacted in situ with calcium andmagnesium salts of naturally-occurring grains and is rendered oil-wet bythe addition" I of oil thereto. As distinguished from the previouspractice the fllm coating is an adsorption film and not a coating formedby chemical or physical precipitation and the wetting compound may ormay not be water-insoluble so long as it forms an adsorption film whichis oilwettable and crude-oll-lnsoluble. This oil-,wet-

table adsorption film coating is probably caused by the placement of asingle molecular layer of the compound upon the face of the sand grainswith the formation of a secondary valence bond between the surface ofthe sand grain and the active portion of the compounds molecule, leavingthe inactive portion of the molecule outwardly oriented on the sandface. The outwardlyoriented portion of the molecule possessesa greateramni'ty for petroleum 011 than for id water and therefore facilitatesthe passage of oil past the filmed sand grain to the exclusion of water.

In accordance with the present invention it has been found thatoil-insoluble polyvalent metal salts of low molecular weight fatty acidspossess the property of forming an oil-.wettable adsorption film coatingupon water-wet sands. These compounds when injected into the oilproducing sands adjacent the Wellbore displace the water film around thesand grains of the waterwet sand and form a molecular film over the sandgrain, with the organic portion or the molecule thought to be outwardlyoriented. Since the films are of molecular thickness the capillaryopenings between the sand grains are not reduced in size and the normalflow of fluids through these capillaries is not resisted. Among thecompounds found .most suitable for the purposes of the invention are theoil-insoluble lead,

as magnesium, mercury and zinc salts of acetic, pro- Opionic and butyricacids and in particular, the

lead salts, such as lead acetate. Preferably, the polyvalent metal saltsoflow molecular weight fatty acids, which are resistant to rapidhydrolysis in the presence of water,. are used. These compounds areintroduced into the formations in dilute neutral or alkaline solutionsranging in concentration from 1-5% by weight.

. Where the compound is water-soluble an aqueous solution is used, butin the case of the waterinsoluble compounds, such as lead butyrate, anacetone or other organic solvent solution is used. In practicalapplications to a well the dilute solution of the polyvalent metal saltto be used 50 is either pumped or poured in from the surface, dependingupon the normal bottom hole pressure of the well. After the solution hasbeen in contact with the sand for a short time it is driven back intothe sand formation by either pumping 55 or otherwise introducing oilinto the well bore.

In those cases where the bottom hole pressure is relatively low, oil maybe driven into the sand by merely'filling the well bore with oil andpermitting it to flow book into the sand. In other cases where the wellis flowing under its own pressure it may be necessary to pump theoil-wetting solution and the 011 back under pressure. In all cases theoil is injected under sufllclent pressure to displace the oil-wettingsolution and oil-wet the sand grains adjacent the well bore.

Prior to the introduction of the above-mentioned solutions in the well,the producing sand may be pretreated as disclosed and claimed inmycopending application Serial No. 212,972, filed June 10, 1938, byflushing to remove fine clay particles and silt from the interstices andpore space of the'sand. This may be accomplished by introducing a chargeof an aqueous alkaline solution of a meta phosphate such as sodiumhexametaphosphate, which also may contain a bufler salt or salt mixtureand a clay dispersing colloidal agent of the character of alkali metalsalts of organic acids, such as tannic acid, gallic acid, and the like.-This flushing treatment may also be modified in accordance with themethod of flushing described and claimed in my copending applicationSerial No. 301,754, filed October 28, 1939, now United States Patent No.2,246,726, which describes and claims a preliminary flushing of theproducing sand with an aqueous alkaline solution containing a claydispersing agent or calcium sequestering agent, or both, or thecombination of either or both with a wetting agent.-

In addition to the flushing treatments specified above, or in lieuthereof, the sand may be pretreated by dehydrating the same to removewater from the pore space, as disclosed'and claimed in my copendingapplication Serial No. 212,974, filed June 10, 1938, now United StatesPatent No. 2,241,253. This may be accomplished by blowing with a heatedgas under pressure, by electrical heaters or heated bodies lowered intothe well opposite the producing sand, by a combination of I theelectrical heaters or heated bodies with the fiow of gas under pressure,or by'the use of a chemical dehydrating agent. A suitable method ofchemically dehydrating the producing sand is that disclosed and claimedin my copending application Serial No. 212,976, filed June 10, 1938, nowUnited States Patent No. 2,248,725, in which the sand is first flushedwith oil and then with a mixture of 'oil and an aliphatic ke'tone, suchas acetone, and finally,- with a solution of an acid' anhydride, such asacetic anhydride, in oil, preferably containing a small amount of asuitable 2, 1,254, wherein, after the deposition of theoil-wettablefilmupon thesand grains, thecoated oussolution containing054.0% of either sodium tetraphosphate or hexametaphosphate, and from.2.5% of an emulsifying agent, such as a sulfonated mixture of minerallubricating oil and benzene, which solution is alkaline to a'pH of about9 or more, is pumped into the formation surrounding the well screen.This washing solution removes finely-divided clay particles and siltfrom the pores of the sand, reduces the surface tension of the contactbetween oil and water and raises the alkalinity of the sand grainsurfaces preparatory to the selective wetting treatment. A large volumeof oil is then pumped in to force the water of the formation and thatintroduced in the washing solution. back into the pores of the sand, soas to reduce the pore space water to a minimum in the immediate vicinityof the well bore. After this step a fresh 2-5% aqueous solution of leadacetate is pumped in.

This solution passes through the sand without leaving any materials toblock the pores and deposits on the wet sand surface an adsorption filmcoating of lead acetate. As mentioned previously, other solutions may beused, and it is to be noted that when using solutions of hydrolyzablemetal salts the solution must be prepared fresh and pumped inimmediately thereafter. The formed film coating is then rendered oil-wetby the addition of a large amount of oil which drives all the previousagents deep into the sand bed and oil-wets the sand grains adjacent thewell bore. This may 'be followed by a dehydration step, such as theblowing of the formation with hot gas, air, or oil vapors. The lasttraces ofwater may thus be replaced by oil, at least in the immediatevicinity of the well bore, to render the sand more permanently oil-wet,and to assist in drying swelled clay and shale fragments. The well isthen placed back on production.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit amscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

What I claim is:

1. The method of treating a water-wet oilproducing sand to render thesand more permeable to oil and less permeable to water, which comprisesdepositing upon the sand grains an oil insoluble film coating of apolyvalent metal salt of a low molecular weight fatty acid and wettingsaid fllm coating with petroleum oil.

2. The method of claim-1 in which the low molecular weight fatty acid isselected from the group consisting of acetic, propionic and butyricacids.

v decrease the production of water, which comprises injecting into thesand adjacent. the well here a 1-6% solution of an oil insolublepolyvalent metal salt of a low molecular weight fatty sand is furtherdehydrated by blowing with heated gas under, pressure or with electricalheaters or heated bodies and the like, and then flushing thedehydrated'sand with oil containing a hydrophobic' colloid, such asfinely-divided asphalt, tar, acids, graphite and the like.

As a specific example of the method of Op ration according to thepresent invention, an'aque- 'meable to oil' and less permeable to water,which comprises injecting 'into the oil producing sand 81 01M101! of ametal salt 01a low molecular assaaoe i weight fatty acid selected fromthe group consisting of the lead, magnesium, zinc, and mercury salts oflow rwlecular weight fatty acids.

7. The method of jreating an oil well to render a water-wet producingsand more permeable to oil and less permeable to-water, which comprisesinjecting into the oil producing sand a solution of alead salt of a lowmolecular weight fatty acid.

8. The method of treating an oil well to render a water-wet producingsand more permeable to oil and less permeable to water, which comprisesinjecting into the oil' producing sand an aqueous solution of awater-solublemetal salt of a low molecular weight fatty acid selectedfrom the group consisting of water-soluble lead, magnesium, zinc, andmercury salts of low molecular weight fatty acids.

9. The method of treating an oil well to render a water-wet producingsand more permeable to oil and less permeable to water, which comprisesinjecting into the oil producing sand an aqueous solution of leadacetate.

ill. The method of treating any oil well to render a water-wet producingsand more permeable to oil and less permeable to water, which compriseswashing the producing-sand adjacent the well bore with an alkalineagueous washing solution, forcing through said sand adjacent the wellbore petroleum oil to force the water away from the well bore,introducing into the sand a 24% aqueous solution of lead acetate, andthen forcing into the sand a petroleumoli to oil-wet the sand adjacentthe well bore.

11. The method of treating anoii well to render 9. water-wet producingsand more permeable to oil and less permeable to water, which com--prises washing the producing sand adjacent the wellbore with an 1 eaqueous washing solution comprising sodium hexametaphosphate and anemulsifying agent, forcing through said sand adjacent the well borepetroleum oil to force the water away from the well bore, introducinginto the sand a 2-5% aqueous solution of lead acetate, and then forcinginto the sand a petroleum oil to oil-wet the sand adjacent the wellbore. 1

12. The method of treating a water-wet oil producing sand to render thesand more permeable to oil and less permeable to water, which comprisesdehydrating the sand to remove water from the pore space thereof,depositing upon the sand grains an oil insoluble film coating of apolyvalent metal salt of a low molecular weight fatty acid, and wettingsaid film coating with petroleum oil.

13. The method of treating an oil well to render a water-wet producingsand more permeable to oil and less permeable to water, which comprisesdehydrating the oil producing sand to remove water from the pore spacethereof, injecting into the sand a solution of a metal salt of a lowmolecular weight fatty acid selected from the group consisting of lead,magnesium, zinc, and mercury salts of low molecular weight fatty acids,and then forcing into the sand a petroleum oil to oil-wet the sandadjacent the well bore.

14. The method of treating an oil well to render 9. water-wet producingsand more permeable to oil and less permeable to water, which comprisesdehydrating the oil producing sand to remove water from the pore spacethereof, injecting into the sand an aqueous solution of lead acetate,and then forcing into the send a petroleum oil to oil-wet the sandadjacent the weilbore.

ALLEN D. G

